Separation of aromatic hydrocarbons



Feb. 11, 1969 B M ET AL 3,427,362

SEPARATION OF AROMATIC HYDROCARBONS Filed Oct. 19. 1966 INVENTORS RODNEYD. BECKHAM EARLE C. MAKIA ATTORNEY United States Patent 3,427,362SEPARATION OF AROMATIC HYDROCARBONS Rodney D. Beckham and Earle C.Makin, St. Louis, Mo.,

assignors to Monsanto 'Company, St. Louis, Mo., a corporation ofDelaware Filed Oct. 19, 1966, Ser. No. 587,930 US. Cl. 260-674 Int. Cl.C07c 7/10, 15/10; B0ld 11/00 9 Claims ABSTRACT OF THE DISCLOSURE Thepresent invention relates to a process for the separation andpurification of aromatic hydrocarbons. More particularly, the presentinvention relates to the process for the separation of vinyl aromatichydrocarbons, i.e., styrene, from alkyl aromatic hydrocarbons, i.e.,xylenes and ethylbenzene.

The term vinyl aromatic hydrocarbons, as used herein, refers to aromatichydrocarbons containing a monoethylenically unsaturated aliphaticsubstituent, e.g., styrene, a-methylstyrene, b-methylstyrene, vinyltoluene. Alkyl aromatic hydrocarbons, as used herein, refers to thosearomatic hydrocarbons having saturated aliphatic substituents, e.g.,xylene, ethylbenzene and the like.

One of the most diflicult separations problems existing in industrytoday is that of separating vinyl aromatic hydrocarbons from closeboiling alkyl aromatic hydrocarbons. In most instances, separation ofsuch hydrocarbons is difiicult at best by distillation. However, torender the problem more difficult, the unsaturated vinyl aromatichydrocarbons are usually easily polymerized and thus tend to polymerizeand foul the equipment used for separation by distillation. Probably themost exemplary and commonly encountered difliculty separable vinylaromatic hydrocarbons and alkyl aromatic hydrocarbons are styrene ando-xylene. These two compounds are very ditlicult to separate one fromanother and because of the entirely dilferent uses of the two, either isan undesirable contaminant in the other and thus it is desired to havemeans for effectively separating the two.

In addition to distillation, it is known that such compounds as mercuricchloride, mercuric acetate, and the like, will complexe with styrene.Such complex formation offers a means of separating styrene fromo-xylene. However, additional and improved separations of this type aredesired. Further, it is often quite diflicult to recover the vinylaromatic hydrocarbons from the complex. Severe conditions usuallynecessary for recovering the complexed vinyl aromatic hydrocarbons fromthe complex often result in substantial polymerization and loss of thevinyl aromatic hydrocarbons.

It is now an object of the present invention to provide a new andimproved process for the separation of aromatic hydrocarbons. A furtherobject of the present invention is to provide a new and improved processfor the separation of vinyl aromatic hydrocarbons from alkyl aromatichydrocarbons. An additional object of the present invention is toprovide a new and improved process for the separation of vinyl aromatichydrocarbons from alkyl aromatic hydrocarbons wherein the vinyl aromatichydrocarbons ice can be substantially totally recovered. Yet anotherobject of the present invention is to provide a process for theseparation of vinyl aromatic hydrocarbons from alkyl aromatichydrocarbons which as a benefit thereof provides a means whereby olefinsand/or conjugated diolefins may be eifectively removed from admixturewith non-conjugated diolefins. Another object of the present inventionis to provide a new and improved process for the separation of styrenefrom o-xylene. Additional objects will become apparent from thefollowing description of the invention herein disclosed.

The present invention which fulfills these and other objects, is aprocess for the separation of vinyl aromatic hydrocarbons from aromatichydrocarbon mixtures containing vinyl aromatic hydrocarbons in admixturewith alkyl aromatic hydrocarbons, which comprises contacting saidaromatic hydrocarbon mixture with an aqueous solution of a silver saltselected from the group consisting of silver fluoroborate, silverfiuorosilicate and mixtures thereof, separating an extract fractioncontaining said aqueous solution of a silver salt and the aromatichydrocarbons absorbed therein, and a ratfinate fraction containingaromatic hydrocarbons not absorbed by said aqueous solution of a silversalt, and recovering from said extract fraction an aromatic hydrocarbonfraction substantially richer in vinyl aromatic hydrocarbons than theinitial aromatic hydrocarbon mixture.

As a particularly useful mode of operating the process of the presentinvention, the aromatic hydrocarbon mixture containing vinyl aromatichydrocarbons and alkyl aromatic hydrocarbons is contacted with theaqueous solution of the silver salt and the resulting mixture of aqueoussilver salt solution and aromatic hydrocarbons then contacted with asaturated aliphatic hydrocarbon of 3 to 15 carbon atoms. Contacting ofthe mixture of aromatic hydrocarbons and aqueous silver salt solutionwith the saturated aliphatic hydrocarbons greatly facilitates theseparation of the non-absorbed aromatic hydrocarbons from the aqueoussilver salt solution and aromatic hydrocarbons absorbed therein. Thesaturated aliphatic hydrocarbons are not absorbed to any extent by theaqueous silver salt solution and act as a selective solvent for thearomatic hydrocarbons not absorbed and held by the aqueous silver saltsolution. When the saturated aliphatic hydrocarbons are contacted withthe mixture of aromatic hydrocarbons and aqueous silver salt solution inaccordance with the process defined herein, extract and rafiinate phasesreadily form, which phases may be easily separated.

The recovery of the vinyl aromatic hydrocarbons from the aqueous silversalt solution extract phase may be accomplished by any available means.The vinyl aromatic hydrocarbons may be distilled from the extract phase.However, it is generally desired to carry out such a distillation underreduced pressure to avoid high temperatures which would likely causepolymerization of the vinyl aromatic hydrocarbons. When distillation isused as the means of recovering the vinyl aromatic hydrocarbons from theaqueous silver salt solution, reduced pressures within the range of to300 mm. Hg are preferred.

A particularly useful method of recovering the vinyl aromatichydrocarbons from the aqueous silver salt solution extract phasecomprises contacting such extract phase with an unsaturated aliphatichydrocarbon selected from the group consisting of olefins, conjugateddiolefins and mixtures thereof. It has been found that the olefinsand/or conjugated diolefin when in excess will displace the vinylaromatic hydrocarbons from the aqueous silver salt solution and are inturn preferentially absorbed and held therein. The olefins and/orconjugated diolefins may be removed from the aqueous salt solution bydistillation under usually significantly less stringent conditions oftemperature and pressure than those required for the removal of vinylaromatic hydrocarbons. However, quite surprisingly, the olefins and/orconjugated diolefins, as the case may be, may in turn be displaced fromthe aqueous silver salt solution by contact with an excess of vinylaromatic hydrocarbons. In view of the ability of the olefins and/orconjugated diolefins to displace the vinyl aromatic hydrocarbons and inturn the vinyl aromatic hydrocarbons to displace the olefins and/orconjugated diolefins from the aqueous silver salt solution, the presentinvention in a particularly useful embodiment provides a dual processwhereby vinyl aromatic hydrocarbons may be separated from alkyl aromatichydrocarbons and olefins and/or conjugated diolefins such as isoprene,may be separated from nonconjugated diolefins, saturated hydrocarbons,etc., using the same solvent solution and, if desired, the same orsubstantially the same equipment. Such a dual process comprises (1)contacting a mixture of aromatic hydrocarbons containing vinyl aromatichydrocarbons and alkyl aromatic hydrocarbons with an aqueous solution ofa silver salt selected from the group consisting of silver fluoroborate,silver fiuorosilicate and mixtures thereof, (2) separating a firstrafiinate fraction containing the nonabsorbed aromatic hydrocarbons anda first extract fraction containing the aqueous silver salt solution andthe aromatic hydrocarbons absorbed therein, (3) contacting said firstextract fraction with a mixture of hydrocarbons containing olefinsand/or conjugated diolefins and nonconjugated diolefins and/ orsaturated hydrocarbons and/ or other hydrocarbons, the quantity of saidmixture of hydrocarbons being such that the olefins and/or conjugateddiolefins are in molar excess to said vinyl aromatic hydrocarbonscontained in said first extract fraction, thereby displacing thearomatic hydrocarbons absorbed in said first extract fraction andforming a second extract fraction comprising said aqueous silver saltsolution and the unsaturated aliphatic hydrocarbons absorbed therein anda second raifinate fraction comprising the hydrocarbons not absorbed bysaid aqueous silver salt solution and the aromatic hydrocarbonsdisplaced from said first extract fraction, (4) separating said secondraffinate fraction and said second extract fraction and (5) recycling atleast a part of said second extract fraction to step (1) above as asubstitute for at least a part of said aqueous silver salt solution andthereafter continuously repeating the above steps.

To further describe the above disclosed dual process of the presentinvention which provides for the separation of vinyl aromatichydrocarbons from alkyl aromatic hydrocarbons and also for theseparation of olefins and/or conjugated diolefins from non-conjugateddiolefins and other hydrocarbons, reference is made to the accompanyingdrawing which is a diagrammatic presentation of a particularly usefuland practical method of carrying out the dual process of the presentinvention. With reference to the drawing, an aromatic hydrocarbonmixture containing vinyl aromatic hydrocarbons and alkyl aromatichydrocarbons is introduced into a liquid-liquid extraction column bymeans of line 11. Concurrently with the introduction of the aromaticmixture by line 11, a solvent solution comprised of an aqueous solutionof a silver salt which is either silver fluoroborate, silverfiuorosilicate, or combinations thereof, is introduced into column 10 bymeans of line 12. The aqueous silver salt solution introduced by line 12will generally contain in addition to the aqueous silver salt solution,olefins and/or conjugated diolefins which have been absorbed therein asdescribed below. If desired, however, some fresh aqueous silver saltsolution may be introduced into line 12 by means of line 13. Lines 11and 12 generally will intersect column 10 at a point near but below thetop of column 10 and at substantially the same distance from the top ofcolumn 10. It is relatively important in this embodiment, that lines 11and 12 be so arranged that the compositions introduced thereby will beintimately co-mingled one with another, almost immediately uponintroduction into column 10. Concurrently with the introduction of thearomatic hydrocarbon mixture through line 11 and the solvent solutionthrough line 12, a saturated aliphatic hydrocarbon of 3 to 15 carbonatoms is introduced into collumn 10 by means of line 14. This aliphatichydrocarbon flows upwardly through column 10 and countercurrentlycontacts the descending mixture of solvent solution and aromatichydrocarbon feed. A rafiinate phase is continuously taken overhead fromcolumn 10 by means of a line 15 through which the raifinate phase ispassed to a distillation or other recovery means (not shown) whereby thecomponents of the raffinate are separated. The components of theraffinate in the continuous operation of the process, comprise thealiphatic hydrocrabon, the aromatic hydrocarbons not absorbed by thesolvent solution and the unsaturated aliphatic hydrocarbons which werecontained in the solvent solution at the time of its introduction intocolumn 10 through line 12.

An extract phase is continuously removed from column 10 by means of line16. This extract phase comprises the aqueous silver salt solution andaromatic hydrocarbon components of the aromatic hydrocarbon mixturewhich dissolves therein. The extract phase is then introduced into asecond liquid-liquid extraction column 17. In column 17, the extractphase from column 10 passes downwardly countercurrently contacting anupfiowing unsaturated aliphatic hydrocarbon feed mixture comprised ofolefins and/or conjugated diolefins and non-conjugated diolefins and/ orother hydrocarbons which are introduced into column 17 by means of line18, and an up-flowing saturated aliphatic hydrocarbon of 3 to 15 carbonatoms which is introduced into column 17 by means of line 19. The secondrafiinate phase is continuously taken overhead from column 17 by meansof line 20. This second rafiinate phase is carried by line 20 todistillation or other recovery means (not shown) whereby the componentsof the second raffinate phase are separated. These components of thesecond rafiinate phase comprise the saturated aliphatic hydrocarbon, thenon-absorbed portion of the hydrocarbon feed mixture, and the aromatichydrocarbons which were contained in the first extract phase at the timeof its introduction by means of line 16 into column 17.

By means of line 21, an extract phase, referred to as the second extractphase, is removed from column 17 and returned through line 21 to line 12for re-use in column 10. This second extract phase is comprised of anaqueous silver salt solvent solution and unsaturated aliphatichydrocarbons absorbed therein.

Those skilled in the art will readily appreciate that many medicationsof the above-described dual process of the present invention and thearrangement of equipment therefor, may be made. However, so long as suchmodifications depend upon the principles and concepts above discussed,such modifications may be practiced without departing from the spiritand scope of the present invention.

To further describe and to specically illustrate the present invention,the following examples are presented. These examples are not to beconstrued as in any manner limiting the present invention.

EXAMPLE I One hundred and ninety grams of a mixture consisting of 89.0grams o-xylene, 99.7 grams styrene and 1.3 grams of other hydrocarbonimpurities were agitated with 3500 ml. of a 47% aqueous silverfiuoroborate solution (specific gravity 1.5999) at a temperature of -25C. The resulting solution was then thoroughly agitated with 210 ml.(138.4 grams) of n-hexane. The agitation was stopped and a rafiinate andextract phase allowed to form. The extract and rafiinate phases werethen separated. The raffinate phase contained the n-hexane and thearomatic hydrocarbons which were not absorbed by the aqueous silverfluoroborate solution, while the extract phase contained the aqueoussilver fiuoroborate solution and the aromatic hydrocarbons absorbedtherein. The aromatic hydrocarbons in the extract and raflinate phaseswere recovered and analyzed. The following table represents the weightpercent composition of the aromatic hydrocarbon feed, the aromatichydrocarbon rafiinate, and the aromatic hydrocarbon extract.

One hundred and ninety grams of a mixture of 90.2 grams of o-xylene and99.8 grams of styrene were thoroughly agitated with 3500 ml. of the 47%aqueous silver fluoroborate solution of Example I at a temperature of 25C. The resulting solution was then agitated with 200 ml. of n-hexane.Agitation was stopped and an extract and raffinate phase allowed toform. The extract and rafiinate phases were then separated and thearomatic hydrocarbons contained in each recovered. To recover thearomatic hydrocarbons absorbed by the silver fiuoroborate solution, theextract phase was subjected to distillation at a temperature of 51 to 63C. and a pressure of 95 to 102 mm. absolute. The overhead from thisdistillation which was the aromatic hydrocarbons contained in theextract phase and the aromatic hydrocarbons recovered from the raflinatephase were subjected to analysis. The weight percent composition of theoriginal aromatic hydrocarbon feed and the aromatic hydrocarbonraflinate and aromatic hydrocarbon extract are presented in thefollowing table.

The total recovery of styrene was approximately 67.4% of that available.

EXAMPLE III Five hundred and fifty grams of a mixture of 259.6 gramso-xylene and 290.4 grams styrene were thoroughly agitated with 10,500ml. (16,795 grams) of the 47% aqueous silver fluoroborate solution ofExample I at a temperature of about 24 C. The resulting solution wasthen thoroughly agitated with 600 ml. of n-hexane. Agitation of thismixture was stopped and an extract and raffinate phase allowed to form.The extract and raflinate phases were then separated. The extract phasewas diluted with 500 m1. of Water and then subjected to distillation ata temperature of approximately 54 C. and a pressure of 95 mm. absolute.About 6000 ml. of distillate was obtained as an overhead from thisdistillation and was extracted with 500 m1. of benzene to insurecomplete recovery of aromatic hydrocarbons from the distillate. Thearomatic hydrocarbons from the distillate and those from the raflinatephase were then subjected to analysis. The following table presents theweight percent composition of the original feed mixture and the aromatichydrocarbon rafiinate and aromatic hydrocarbon extract.

The above represents a rafiinate yield of styrene of 71.1 grams (24.5%of that available) and the extract distillate yield was 198.1 grams(68.2% of that available) equivalent to a 92.7% recovery of theavailable styrene in the original feed.

EXAMPLE IV A mixture of 90.2 grams o-xylene and 99.8 grams styrene wasthoroughly agitated with 3500 ml. (5598 grams) of the 47% aqueous silverfluoroborate solution of Example I at a temperature of approximately 24C. The resulting mixture 'was then thoroughly agitated with 200 ml. ofhexane. Agitation was stopped and an extract and rafiinate phase allowedto form. The extract and raifinate phases were then separated. Followingthe separation, the extract phase was then contacted with 1360 grams ofisoprene which displaced the aromatic hydrocarbons contained in theextract phase and formed a new extract phase containing the aqueoussilver fluoroborate solution and isoprene. The displaced aromatichydrocarbons were then separated from the new extract. Next, the newextract was brought into contact with 1890 grams of styrene whichdisplaced the isoprene from the new extract and resulted in formation ofstill another extract containing the aqueous silver fluoroboratesolution and styrene. The aromatic hydrocarbons from the rafiinatephase, the aromatic hydrocarbons displaced from the first extract phaseand the isoprene displaced from the second extract phase were subjectedto analysis. The weight percent composition of the original aromatichydrocarbon feed and these various fractions is presented in thefollowing table.

TABLE Wt. percent Styrene o-Xylene Isoprene Aromatic Hydrocarbon Feed52.55 47.45 Aromatic Hydrocarbon Raf nate- 23.01 76.99 Aromatic FractionDisplaced by Isoprene 90.51 9.45 Isoprene Fraction Displaced by StyreneThe above procedure resulted in the recovery of of the available styrenefrom the original aromatic hydrocarbon feed in the respective puritiesset forth in the above table.

The aqueous silver salt solutions used in the process of the presentinvention include the silver salts, silver fluoroborate, and silverfluorosilicate. These silver salts may be used alone or in combination.The preferred silver salt is the silver fluoroborate. Usually, theaqueous silver salt solution will contain the silver salt in aconcentration of 30 to 60% by weight of the solution. Preferred,however, are concentrations of 45 to 55% by weight.

In carrying out the process of the present invention, most often about10 to 70 parts by weight of aqueous silver salt solution by part byweight of vinyl aromatic hydrocarbons in the aromatic hydrocarbonmixture to be separated are employed. Preferably, however, the amount ofaqueous silver salt solution used is within the range of 20 to 50 partsby weight by part by weight of vinyl aromatic hydrocarbons. Usually, thegreater the concentration of the silver salt in the aqueous silver saltsolution, the less the amount of the salt solution required. However,regardless of the concentration of the silver salt within the silversalt solution, so long as it is within the above-defined concentrations,the amount of aqueous silver salt solution used will be within the aboveranges.

When olefins and/ or conjugated diolefins are employed to displace thevinyl aromatic hydrocarbons from the aqueous silver salt solution or theprocess of the present invention is operated as a dual process, as abovedescribed, it is generally desirable that the amount of olefins and/ orconjugated diolefins contacted with the vinyl aromatic hydrocarboncontaining aqueous silver salt solution be in weight ratio to theaqueous silver salt solution within the range of from 10:1 to 70:1,preferably within the 7 range of from 20:1 to 50:1. Within these ranges,however, it is necessary that the amount of olefin and/ or conjugateddiolefin employed always be greater on a molar basis, than the amount ofvinyl aromatic hydrocarbons contained in the aqueous silver saltsolution.

The aromatic hydrocarbon mixture containing vinyl aromatic hydrocarbonsand alkyl aromatic hydrocarbons which are to be separated in accordancewith the present invention is generally contacted with the aqueoussilver salt solution at a temperature within the range of 30 to 70 0.,preferably 20 to 50 C. Pressure does not appear to be critical in theselective absorption of the vinyl aromatic hydrocarbons by the aqueoussilver salt solution. Therefore, the pressure at which the process ofthe present invention is operated is generally based upon practicality.

The period of contact of the aromatic hydrocarbon mixture to beseparated with the aqueous silver salt solution may be very short sinceabsorption of the vinyl aromatic hydrocarbons by the aqueous silver saltsolution is generally almost immediate. As a practical matter, theperiod of contact will vary somewhat depending upon the efliciency ofthe means employed for contacting the aromatic hydrocarbons with theaqueous silver salt solution. The determination of the optimum periodsof contact are well within the ability of those skilled in the art andthus require no discussion herein.

When the process of the present invention is operated as a dual processor conjugated diolefins are used to displace and recover the vinylaromatic hydrocarbons from the aqueous silver salt solution, the sameconditions as to temperatures, pressures and contact time may be used asare used for contact of the aromatic hydrocarbons with the aqueoussilver salt solution.

It has been found particularly useful in carrying out the process of thepresent invention to use saturated aliphatic hydrocarbons of 3 to 15carbon atoms per molecule to extract the non-absorbed aromatichydrocarbons from the aqueous silver salt solution. As noted above, theuse of the saturated aliphatic hydrocarbons of 3 to 15 carbon atomsgreatly facilitates the formation of an extract and ratfinate phase andthus considerably simplifies the present separations process.Non-limiting examples of such hydrocarbons are propane, n-butane,n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane,n-undecane, n-dodecane, n-tridecane, isobutane, isopentanes,isoheptanes, isodecanes, isododecanes, isotridecane, cyclopentane,cyclohexane, methylcyclohexane, cycloheptane, and the like. Most often,the saturated aliphatic hydrocarbons are paraffinic hydrocarbons and maybe straight-chain or branched-chain. The most useful saturated aliphatichydrocarbons are the paraffinic hydrocarbons of 4 to 7 carbon atoms permolecule.

The amount of saturated aliphatic hydrocarbons of 3 to 15 carbon atomsused in the process of the present invention may vary considerably. Theactual amount of such aliphatic hydrocarbon used will depend to a largeextent on the amount of alkyl aromatic hydrocarbons in the aromatichydrocarbon mixture and the degree of separation desired, etc. Usually,however, about 0.5 to 10 volumes of saturated aliphatic hydrocarbon willbe used per volume of alkyl aromatic hydrocarbon in the aromatichydrocarbon feed mixture to be separated. Preferably, however, about 1to 3 volumes of the saturated aliphatic hydrocarbon will be used pervolume of alkyl aromatic hydrocarbons in the feed mixture.

In employing the saturated aliphatic hydrocarbons of 3 to carbon atomsto remove the unabsorbed alkyl aromatic hydrocarbons from the silversalt solution, these aliphatic hydrocarbons may be contacted with themixture of aqueous silver salt solution and aromatic hydrocarbonsabsorbed therein after the initial contact and agitation of the aromatichydrocarbon feed with the silver salt solution has ceased or thesaturated aliphatic hydrocarbon may be brought into contact with theaqueous silver salt solution concurrently with the aromatic hydrocarbonfeed which is to be separated. Further, the saturated aliphatichydrocarbon may be introduced concurrently with the aromatic hydrocarbonmixture to be separated into countercurrent contact with the aqueoussilver salt solution. Instead, however, the saturated aliphatichydrocarbons may be contacted countercurrently with the aromatichydrocarbon mixture to be separated and the aqueous silver saltsolution.

The aromatic hydrocarbon mixtures which may be separated in accordancewith the present invention are those containing vinyl aromatichydrocarbons and alkyl aromatic hydrocarbons. While the presentinvention is operable in separating a wide range of such hydrocarbons,it is most practical for the separation of aromatic hydrocarbon mixturescontaining vinyl aromatic hydrocarbons and alkyl aromatic hydrocarbonswithin the C to C range. The present invention is particularly usefuland practical for the separation of styrene from close boiling o-xyleneand for the separation of a-methylstyrene and/or vinyl toluene fromclose boiling alkyl aromatic hydrocarbons.

The olefins and/or conjugated diolefins useful in dislacing absorbedvinyl aromatic hydrocarbons from the aqueous solution of a silver saltare preferably those containing 2 to 8 carbon atoms per molecule thoughthose having higher numbers of carbon atoms may be used. These olefinsand/ or conjugated diolefins may be in relatively pure state or may bein admixture with other hydrocarbons such as parafiins, naphthenes oreven alkyl aromatic hydrocarbons. While the olefins and/or conjugaterdiolefins may be cyclic, straight-chain or branched-chain in structure,it is preferable that they be straight or branched-chain. Usually, theconjugated di olefins are preferred over the olefins. When the presentinvention is operated with :a C to C aromatic hydrocarbon feed mixturecontaining vinyl aromatic hydrocarbons, isoprene or other conjugateddiolefins of 5 to 7 carbon atoms are particularly useful.

What is claimed is:

1. A process for the separation of vinyl aromatic hydrocarbons fromaromatic hydrocarbon mixtures containing 'vinyl aromatic hydrocarbons inadmixture with alkyl aromatic hydrocarbons, which comprises contactingsaid aromatic hydrocarbon mixture with an aqueous solution of a silversalt selected from the group consisting of silver fiuoroborate, silverfluorosilicate and mixtures thereof, separating an extract fractioncontaining said aqueous solution of a silver salt and the aromatichydrocarbons dissolved therein, and a railinate fraction containingaromatic hydrocarbons not absorbed by said aqueous solution of a silversalt, and recovering from said extract fraction an aromatic hydrocarbonfraction substantially richer in vinyl aromatic hydrocarbons than theinitial aromatic hydrocarbon mixture, by contacting said extractfraction with an amount of an unsaturated aliphatic hydrocarbon selectedfrom the group consisting of olefins and conjugated diolefins such thatsaid unsaturated aliphatic hydrocarbon is in molar excess to the vinylaromatic hydrocarbons contained within said extract fraction.

2. The process of claim 1 wherein the silver salt in said aqueoussolution of a silver salt comprises approximately 30 to 60 percent byweight of said solution.

3. The process of claim 1 wherein the amount of aqueous silver saltsolution contacted with said aromatic hydrocarbon mixture is such as tocause a ratio by weight of aqueous silver salt solution to vinylaromatic hydrocarbons in said aromatic hydrocarbon mixture within therange of about 10:1 to 70: l.

4. The proces of claim 1 wherein the aromatic hydrocarbon mixture is onecontaining vinyl aromatic hydrocarbons and alkyl aromatic hydrocarbonswithin the C to C range.

5. The process of claim 1 wherein the aromatic hydrocarbon mixture iscontacted with the aqueous silver salt solution at a temperature withinthe range of 30 to 70 C.

6. The process of claim 1 wherein the mixture resulting 'from thecontacting of the aromatic hydrocarbon mixture with the aqueous solutionof the silver salt is contacted with a saturated aliphatic hydrocarbonof 3 to 15 carbon atoms.

7. The process of claim 6 wherein about 0.5 to volumes of said saturatedaliphatic hydrocarbon is used per volume of alkyl aromatic hydrocarbonin the aromatic hydrocarbon mixture which is contacted with the aqueoussilver salt solution.

8. The process of claim 6 wherein the saturated aliphatic hydrocarbon isa non-cyclic paraffinic hydrocarbon of 4 to 7 carbon atoms per molecule.

9. A process for the separation of vinyl aromatic hydrocarbons fromalkyl aromatic hydrocarbons and unsaturated aliphatic hydrocarbonsselected from the group consisting of olefins and conjugated diolefinsfrom mixtures of such unsaturated hydrocarbons with other hydrocarbonswhich comprises (1) contacting a mixture of aromatic hydrocarbonscontaining vinyl aromatic hydrocarbons and alkyl aromatic hydrocarbonswith an aqueous solution of a silver salt selected from the groupconsisting of silver fiuoroborate, silver fluorosilicate and mixturesthereof, (2) separating a first raflinate fraction containing thenon-absorbed aromatic hydrocarbons and a first extract fractioncontaining the aqueous silver salt solution and the aromatichydrocarbons absorbed therein, (3) contacting said first extractfraction with a mixture of said unsaturated aliphatic hydrocarbonsabsorbed therein and a second rafiinate fraction comprising thehydrocarbons not absorbed by said aqueous silver salt solution and thearomatic hydrocarbons displaced from said first extract fraction, (4)separating said second rafiinate fraction and said second extractfraction and, (5) recycling at least a part of said second extractfraction to step (1) above as a substitute for at least a part of saidaqueous silver salt solution and thereafter continuously repeating theabove steps.

References Cited FOREIGN PATENTS 949,095 2/ 1964 Great Britain.

DELBERT E. GANTZ, Primary Examiner.

C. R. DAVIS, Assistant Examiner.

U.S. C1.X.R. 260669

